Wind turbine blades are being made larger for improved economic efficiency. As blade size increases, structural requirements increase to support the greater mass. Additional structural mass results in greater gravitational and centrifugal loads, requiring still more structure in a cascading fashion. Blade designs can devote the majority of their structural strength simply to support the mass of the blade. Due to scaling laws, maximum producible turbine size is limited by this problem. Increased blade mass requires increased mass in all the turbine and tower structural components. So this problem is a large contributor to total turbine cost.
Damping of wind turbine blades is often low due to the natural properties of the materials of construction of the blades. Aerodynamic damping is effective for flapwise loads only. “Flapwise” means perpendicular to the chord and the span of the blade, such as in the direction 36 in FIG. 1. Edgewise loads include gravitational loads and dynamic loads from oscillations. “Edgewise” means parallel to the chord of the blade, such as in the direction 38 of FIG. 1. Edgewise oscillations are minimally damped, as they depend completely on the low levels of material damping. Therefore, edgewise loads due to oscillations are difficult to reduce. They contribute significantly to the total loads.